The overall aim has been, and continues to be, to determine in muscle and nerve cells functional, developmental, and structural correlates, with particular attention to ultrastructural aspects. Our in vitro studies on the self-assembly of the contractile proteins will be expanded to encompass comparative interactions of vertebrate and invertebrate myosins. Hopefully this will complete our understanding of the regulating influence of the myosin cross-bridges in the distribution of myofilaments in the sarcomere. We plan to examine filament distribution in invertebrate neurones using HMM labeling as an important corollary to published studies of physical association between axoplasmic microtubules and membrane-limited components, particularly mitochondria and synaptic vesicles. Identification and structural characterization of synaptic receptor molecules by tannic acid staining will continue, with selected material in which the myoneural junctions are unusually large and readily identified for fine structural work, as in lizard intercostal muscle. Finally, collaborative work with several physiology laboratories (Puerto Rico, Duke Univ.) of transverse tubule and collagen fine structure in Ascaris muscle and echinoderm muscle will be continued.